The invention pertains to a flexible cord-like hollow object with an inner zone, which is enclosed by a casing, for the transportation of media.
Flexible cord-like hollow objects of this generic type are known. These cord-like hollow objects, which are also called tube(s) below, are used in many sectors of industry for the transportation of liquid or gaseous media. For use in technical climate control units, e.g. in motor vehicles, such tubes are used for the transportation of refrigerants. Refrigerants have the property that they are volatile and lead to harmful effects when they get into the earth""s atmosphere. In order to avoid this, use should be made of natural refrigerants, e.g. CO2. In the case of known refrigerant tubes, it is a disadvantage that these are not diffusion-proof and that they exhibit high permeability to natural refrigerants, especially carbon dioxide CO2.
A tube for the transportation of gases is known from DE 40 20 798 A1, whereby this tube has an inner layer that has a low permeability to gases. In addition, a flexible tube for the transportation of media is known from EP 0 375 608 A1, whereby this tube has a barrier layer that is integrated into the casing and that comprises a metal foil, which is arranged to run length-wise or in a spiral shape, whereby the edges of the strip of metal foil overlap. A disadvantageous feature in this regard is that impairment of the impermeability to gases can occur, especially in the event of a high bending stress.
Thus the objective of the invention is to create a flexible cord-like hollow object of this generic type that has low permeability with simultaneously high flexibility, especially in the case of CO2. In accordance with the invention, this objective is accomplished by means of a flexible cord-like hollow object with the characterizing features that are designated in claim 1. As a result of the feature that the casing has a barrier layer on the casing surface that faces the inner zone, whereby the barrier layer comprises sub-elements that are arranged in a scale-like manner and whereby the barrier layer is impermeable to the volatile molecules of the medium that is to be transported, permeation through the flexible cord-like hollow object is prevented or at least reduced to a negligibly small value. Thus it becomes possible to transport refrigerants without the volatile components of the refrigerant being able to get into the atmosphere, especially when, as is preferred, the flexible cord-like hollow objects are used as a refrigerant tube. A low rate of permeation simultaneously ensures the reliable functioning of the refrigeration unit that is to be supplied with the refrigerant. The flexibility of the hollow object is not impaired, or it is impaired only insignificantly, by the scale-like arrangement of the sub-elements. The scale-like arrangement of the sub-elements leads to the situation in which the barrier layer does not break during stressing due to bending. Breakage or damage to the barrier layer would lead to an increase in the rate of permeation.
The scale-like construction can be achieved in a very advantageous manner by producing an appropriate crystal structure during the vapor deposition of the metallic barrier layer that is preferably provided.
The scale-like construction of the crystal structure can preferably be obtained via the vapor deposition of a crystalline substance on a layer of the casing that serves as a carrier layer, whereby the crystalline substance comprises e.g. metal or synthetic material. As a result, crystalline regions (platelets) are produced, which are absolutely impermeable, on the surface of the layer of the casing that serves as the carrier. As a result, the situation is reached in the non-expanded state, i.e. the non-stressed state, that the flexible cord-like hollow object (tube) is almost completely impermeable to the refrigerant that is to be transported. Negligibly low permeation can arise only through extremely small seams between the vapor deposited platelets. If the platelets are vapor deposited in such a way that they overlap, then a degree of overlapping of the platelets can be ensured, even during stressing due to bending or tensile stressing of the tube, so that e.g. 99% of the total surface is covered with the crystalline platelets even in such a state of the tube.
An advantageous feature, in particular, as a result of this is that use can be made of the flexible cord-like hollow objects, which have been provided with these crystalline platelets, even in the high pressure range and their low permeability remains intact. Such high pressure expansion tubes, which have been provided with the barrier layer in accordance with the invention, excel by virtue of their high flexibility, vibration attenuation and favorable effect on acoustics so that these advantages can be exploited along with the simultaneous assurance of low permeability.
In particular, use can be made of carbon dioxide CO2 as the refrigerant in high pressure expansion tubes that have the barrier layer in accordance with the invention. The use of carbon dioxide as the refrigerant in the high pressure range leads, as such, to the problem of so-called decompressive explosion in the event of a sudden drop in pressure. The abrupt formation of large aggregates of the refrigerant occurs in a material that is in contact with the refrigerant. This would lead to damage or, as the case may be, to the destruction of the material. As a result of the barrier layer in accordance with the invention, the situation is now reached in which damage to the material, i.e. the casing of the flexible cord-like hollow object here, cannot occur since permeation into the casing of the molecules of carbon dioxide, which is used as the refrigerant, is prevented. Because of the aforementioned scale-like arrangement of the crystalline platelets, in particular, permeation is prevented or, as the case may be, reduced to a negligible minimum even in the case of high pressure expansion.
Moreover, it is preferable if the barrier layer comprises sub-elements that have been arranged in a scale-like manner, whereby these sub-elements preferably overlap in the direction of transportation of the medium and/or coaxially relative to the longitudinal axis of the hollow object. As a result, an especially flexible arrangement of the barrier layer is achieved that excels by virtue of particularly low permeability depending on the material that is selected [for its construction].
In a preferred form of embodiment of the invention, the feature is provided that the barrier layer comprises metal or synthetic material. As a result, a material can be selected in a simple manner that is in harmony with the refrigerant that is to be transported, whereby the material exhibits especially good barrier action with respect to the volatile components of the medium that is to be transported.
Moreover, the feature is provided in a further preferred form of embodiment of the invention that the barrier layer is connected to the outer casing surface of the inner layer of the casing in a non-positive manner [i.e. in an adherent manner that is force-actuated]. As a result, the situation is reached in which detachment of the barrier layer from the surface of the casing can be prevented during subsequent usage of the flexible cord-like hollow object in accordance with directions so that the low permeability, which has been achieved, is maintained. The feature is preferably provided that the casing surface is treated physically and/or chemically in order to increase the strength of adhesion between the barrier layer and the casing surface. As a result, roughening can be achieved, preferably and in particular, and this ensures better adherent bonding to the subsequently applied barrier layer.
In particular, it is preferred that an increase in the strength of adhesion between the barrier layer and the casing surface be obtained via polarization or activation of the material of the casing at least in the surface region of the casing surface. Depending on the material of the casing, which preferably comprises a polymer, polar groups can be incorporated, as a result, into the basic molecular structure of the casing, whereby these polar groups ensure an improvement in the coating of the casing surface with the barrier layer.
In a preferred form of embodiment of the invention, moreover, the feature is provided in which an additional bonding agent is arranged between the barrier layer and the casing surface. This additional bonding agent leads to an especially strong and durable non-positive [force-actuated, adherent] bond between the barrier layer and the casing so that the adherent bonding between the barrier layer and the casing remains intact even with relatively intense mechanical stressing during usage, which is in accordance with directions, and its low permeability can be maintained.
Further preferred forms of embodiment of the invention result from the remaining characterizing features that are designated in the subsidiary claims.